Not sure how you define sexism, but more traditional patriarchal groups have higher birth rates and more social cohesion. In the long run those traits propagate themselves. The stereotypical cat lady, not so much.
As far as racism, it may not propagate the species but surely it helps propagate those genetically closer to oneself. Isn’t in-group preference pretty common? Don’t need to be EO Wilson or Richard Dawkins to see why.
How do you define sexism? I'm not sure how the "stereotypical cat lady" is even relevant.
> more traditional patriarchal groups have higher birth rates
I don't think we need higher birth rates at this point, with over 8 billion humans on Earth already.
> As far as racism, it may not propagate the species but surely it helps propagate those genetically closer to oneself. Isn’t in-group preference pretty common?
Romantic preferences are not racism. Would you say that failure to be bisexual is sexism? (Spoiler: it's not.)
It's crucial to recognize, though, that romantic preferences are entirely subjective. If you consider your romantic preferences to be objectively superior humans and those who aren't to your preference objectively inferior humans who deserve a lower rank in society, that would be racism and/or sexism.
As far as racism, it may not propagate the species but surely it helps propagate those genetically closer to oneself. Isn’t in-group preference pretty common? Don’t need to be EO Wilson or Richard Dawkins to see why.